Unique Salt-Tolerance-Related QTLs, Evolved in Vigna riukiuensis (Na+ Includer) and V. nakashimae (Na+ Excluder), Shed Light on the Development of Super-Salt-Tolerant Azuki Bean (V. angularis) Cultivars

Abstract

Wild relatives of crops have the potential to improve food crops, especially in terms of improving abiotic stress tolerance. Two closely related wild species of the traditional East Asian legume crops, Azuki bean (Vigna angularis), V. riukiuensis “Tojinbaka” and V. nakashimae “Ukushima” were shown to have much higher levels of salt tolerance than azuki beans. To identify the genomic regions responsible for salt tolerance in “Tojinbaka” and “Ukushima”, three interspecific hybrids were developed: (A) azuki bean cultivar “Kyoto Dainagon” × “Tojinbaka”, (B) “Kyoto Dainagon” × “Ukushima” and (C) “Ukushima” × “Tojinbaka”. Linkage maps were developed using SSR or restriction-site-associated DNA markers. There were three QTLs for “percentage of wilt leaves” in populations A, B and C, while populations A and B had three QTLs and population C had two QTLs for “days to wilt”. In population C, four QTLs were detected for Na+ concentration in the primary leaf. Among the F2 individuals in population C, 24% showed higher salt tolerance than both wild parents, suggesting that the salt tolerance of azuki beans can be further improved by combining the QTL alleles of the two wild relatives. The marker information would facilitate the transfer of salt tolerance alleles from “Tojinbaka” and “Ukushima” to azuki beans.

Diversity of salt tolerance in <i>Vigna nakashimae</i>, wild related species of the azuki bean (<i>Vigna angularis</i>)

“…Six further Vigna species; namely, V. marina, V. luteola, V. trilobata, V. vexillata, V. nakashimae, and V. riukiuensis exhibit salt tolerance up to 200 mM (NaCl) (Iseki et al 2016, Yoshida et al 2020. V. nakashimae and V. riukiuensis are cross compatible with the azuki bean and have different mechanisms of salt tolerance (Noda et al 2022, Ogiso-Tanaka et al 2023, Yoshida et al 2016. V. nakashimae grows in South Korea, northeastern China, Kyushu (Japan), and neighboring remote islands (Tomooka et al 2013).…”